This invention relates to a presswork machine equipped with a detachable bolster and a press die positioning device for positioning and fixing a press die onto the bolster.
A body of an automobile, particularly a monocoque body is formed by welding and joining a large number of body panels. Normally, these body panels are produced from a strip unwound from a coil, which is cut into blanking panels of shapes corresponding to body panels, and the blanking panels are then processed by a transfer press line into the body panels of specified shapes.
As well known, in the press work, the time required for the replacement of press dies is one of the factors that largely affect the operation rate of the pressing facility. Therefore, in view of the adaptability of the press line to the automobile assembly line, it is necessary to process several hundred to several thousand blanking panels using a pair of press dies, the processing work is sequentially carried out for all press dies, and the finished body panels are temporarily stored in a stockyard, which are supplied as needed to the assembly line. Similarly, when the coil is cut into the blanking panels, the coil is punched into several hundred to several thousand blanking panels using a pair of press dies and, while this work is sequentially carried out for all press dies, these blanking panels are continuously supplied to the transfer line.
Currently, only part of handling work of press dies for presswork machines is automated. Handling of press dies between the bolsters for the presswork machines and the press die stockyard is inevitably performed by hanging work using an overhead-travelling crane or the like, because of heavy weight of the press dies.
To attempt automation of a series of press work according to the car production program, it is necessary to abolish handling of press dies by hanging work, and handling of press dies between the bolsters for the presswork machines and the press die stockyard be performed by a stacker crane or the like. In this connection, it is also necessary to facilitate positioning of press dies with respect to the bolsters.
To prevent lowering of operation rate of the presswork machine associated with replacement of press dies, it is desirable to use a pair of bolsters, and replacement of press dies be performed to the bolster which is in the standby state at the side of the presswork machine.
However, prior art bolsters have a device for clamping the lower press die (Japanese Utility Model Laid-open No. 61-133228/1986, Japanese Utility Model Laid-open No. 61-205624/1986). Since such bolsters are loaded in alternation on the presswork machine, various pipes become complex in structure, which leads to increased equipment cost. Since, in the prior art, press dies are placed directly on the top of the bolster, there is no room for inserting a fork of a stacker crane or the like between the bolster and the press dies, making it impossible to automate the handling work of press dies.